Continuity mistake: Season 1 episode 2, Wendigo conflicts with this episode. Originally the wendigo information is printed on the left-hand side of the journal. On the right side is loads of symbols and text. Here the "same" page featuring the wendigo can be seen when Dean and Sam are searching for the asylum information but it's different.
Visible crew/equipment: While Sam Bobby and Dean are talking you can see in the bottom left-hand side a person sitting looking at a camera. (00:17:28)
Revealing mistake: When Max opens the bedroom door to confront his step-mother and Dean, using his telekinesis powers, you can see the equipment used to open the door, a rope pulling the door on the floor. (00:34:19)
Continuity mistake: As Sam is looking for the next victim in his visions, she walks by with her baby in a stroller. The baby is a completely different looking doll the first two times shown, but is blue-eyed Rosie when Sam approaches and interacts with her. (00:12:30)
Continuity mistake: When Sam gets the skeleton heads out of the back of the car, he brings the box in his arms long ways, but when the shot goes back to him it is turned the other way. (00:22:50)
Bloody Mary - S1-E5
Continuity mistake: When Jill's friend is saying how Jill died and mentions her eyes, she has her hands lowered in one shot but raised in the next. (00:16:11)
Continuity mistake: When Dean says he's going to talk to Amanda to get a grip on her mental state he has his head back on the seat and is looking straight ahead. When the shot changes he's now looking at Sam. (00:27:20)
Answer: Angels themselves may not have genitalia, but their vessels do. Nephilim occur when an angel in a vessel reproduces.
Greg Dwyer